The present invention relates to a method for producing functional prototypes using polymeric molds. The polymeric molds are relatively low-cost, dimensionally accurate and rapidly formed. The instant invention has particular utility in the product design and premanufacturing phase in industries, such as automobiles, toys, consumer electronics, and biomedical devices, where rapid prototyping is vital to success.
Prototypes are three dimensional representations of the whole or a component of an article to be manufactured. The prototype may be built to actual size or scaled down. The advantage of prototypes relative to blue prints or even three dimensional renditions on a computer screen is the ability to hold, turn, and feel the actual part. As the complexity of part manufacturing increases, the need to visually inspect an article during its design phase has increased. Given the significant advantages of utilizing a prototype during the initial design phase, it is not surprising that the areas in which prototypes are considered essential continue to grow.
A well-known means for producing a prototype part utilizes laminated polyurethane or epoxy-based modeling boards. The laminated boards have the look, feel and consistency of wood. Prototype models are produced by cutting and shaving away excess board material. The boards are capable of showing exterior surface features and details. Such systems are particularly useful for inspecting relatively large articles. Preparing prototypes from a laminated board requires a great deal of time and experience.
An alternative technology for producing highly accurate and detailed prototypes is stereolithography. A three-dimensional object is produced in a stereolithographic system that contains a resin bath, an irradiating source and a movable support. The movable support is capable of moving vertically within the resin bath. The resin bath contains selected high performance resins that are curable when subjected to ultraviolet radiation. The irradiating source directs its energy at the surface of the resin bath to selectively cure regions of the top layer of resin.
The irradiating source is controlled by a computer. The computer determines the movement and direction of the irradiating source based upon an analysis of a computer-aided design of the desired object. The computer essentially determines the outline of the desired object on a layer by layer basis. The computer then directs the irradiating source to selectively cure regions of the top layer to conform with the outline of each layer. As each layer is completed, the movable support lowers the previously cured layer into the resin bath to allow new resin to overflow the previously cured layer. This process is repeated until the desired object is produced. A thermal postcuring step is usually required to give the resulting cured article sufficient strength.
A similar additive build process is fused deposition modeling, which uses thermoplastic wire-like filaments. The filaments are melted and extruded through a delivery head on a layer-by-layer basis. The extrudate is positioned by the delivery head which follows a computer-aided design layer outline. As the layers are deposited, a platform is lowered that supports the layered extrudate.
A further additive build process is three dimensional printing. Three dimensional printing uses powdered materials, such as refractory powder and a binder material. Three dimensional parts are fabricated by selectively applying binder to a thin layer of refractory powder, which causes the powder to stick together. The layers are formed sequentially in a manner analogous to the previously discussed additive build processes.
Ballistic particle manufacturing produces three dimensional objects using an ink-jet mechanism to deposit a wax-like material on a layer-by-layer basis. A related process utilizes an ink-jet mechanism to deposit molten metal on a layer basis.
Laminated object manufacturing produces three-dimensional objects by laminating layers of trimmed sheet material. The laminated sheets of material are trimmed using a laser. Successive layers of sheet material adhere to one another using heat and pressure to activate a thermal adhesive.
The building processes described above can be utilized to produce the actual prototypes, not molds themselves. For this reason, the building processes described above all suffer from the same shortcoming that only one prototype results from each building cycle.
Lost core molds have been used to produce molds for the actual parts. For example, the automobile industry increasingly uses aluminum engine components to reduce weight and energy consumption in its vehicles while controlling manufacturing costs. But the mechanics of making and assembling cores and molds for conventional casting has limited the designs that could be cast. The process of lost foam casting, in which a Styrofoam pattern immersed in dry sand becomes a metal casting as hot metal vaporizes the plastic foam, allows automotive companies to cast cylinder heads with the complex geometries required for modern internal combustion engines. The cost of producing the tools to create the foam patterns, however, is high and changes in tooling take substantial amounts of time.
Additionally, at least one company proposes to develop a low-cost tool-making machine and associated processes to produce plastic, ceramic, and metal tools for use in automobile manufacturing. The proposed Motor Vehicle Rapid Tool Maker (MVRTM) would use a precision plotter to position a jet to deposit small drops of a xe2x80x9cbuildxe2x80x9d material consisting of a thermoplastic material or a slurry of ceramics or powdered metal. Another jet would deposit a wax that would serve as the xe2x80x9csupportxe2x80x9d material for part bracing and fine definition. Then the model would be trimmed to the desired height and dipped into a solvent to melt the wax. The resulting pattern of xe2x80x9cbuildxe2x80x9d material would be converted to a metal tool through an investment casting or sintering process.
U.S. Pat. No. 5,641,448, assigned to the National Research Council of Canada, discloses a process for making a prototype mold using a stereolithography system. A solid support is provided on the prototype mold to prevent flexing. Additionally, the inner surface of the mold is coated with a thin metal coating. The mold is fitted into an injection molding machine to produce prototype parts at relatively low pressures. U.S. Pat. No. 5,439,622, assigned to Motorola, Inc., also discloses a process for making a prototype mold using a stereolithography system. U.S. Pat. No. 5,458,825, assigned to Hoover Universal, Inc., discloses a process for making blow molding tooling manufactured by stereolithography for rapid container prototyping. U.S. Pat. No. 5,562,846, assigned to Northern Telecom Limited, discloses a process for manufacturing a mold part having a cooling passage in a stereolithography system.
U.S. Pat. No. 4,863,663, assigned to General Motors Corporation, discloses a process for making a motor vehicle component part. A rough model is fabricated of the desired component part from a plurality of interlocking, cut rigid sheet materials. The exterior surfaces defined by the interlocking, cut rigid sheets are coated with a sheet material. The resulting model can be used to make a mold for subsequent manufacture of prototype parts. The mold is constructed by successively layering the resulting model with resin and glass fiber cloth.
U.S. Pat. No. 5,231,749, assigned to John H. Hutchinson, relates to a method of making an interior and exterior design verification model. The material used for making the design model can include clay, REN, wood, composite modeling compounds, high density foam and fiberglass.
U.S. Pat. No. 5,432,322, assigned to Bruder Healthcare Co., relates to an improved heating pad and method for making the same. In one embodiment of said method, a heat element is covered by a continuous layer of outer organic polymer by molding the polymer over the element. A mold is fabricated used REN-Shape(trademark) material, a composite tooling material. After the mold is fabricated, the heating element and associated components are placed in the mold, which is clamped shut. A casting polyurethane composition is then pumped into the mold to encapsulate the unit. The mold is unclamped after cure to remove the overmolded sealed heating pad.
Despite the on-going research endeavors, there exists a need for a system capable of producing multiple, dimensionally accurate and functional prototypes. The system must be flexible to allow multiple design changes without significant time delays. Additionally, the system preferably should produce a prototype using the same material that will be used to produce the final article.
The present invention relates to a method for manufacturing a mold by providing at least one polymeric board material having a glass transition temperature less than the molten temperature of a thermoplastic molding material and removing at least a portion of the polymeric board material to form, according to a computer-aided design, a reverse image of a desired article to be molded. Preferably, at least a portion of the polymeric board material is removed using a high speed CNC machining device. The polymeric board material can be a cured polyurethane-forming composition or a cured mixture containing at least one epoxy resin having, on average, more than one glycidyl group per molecule. The thermoplastic molding material is preferably selected from the group of polypropylene, acrylonitrile-butadiene-styrene copolymer and polycarbonate.
An additional embodiment of the present invention is a method for manufacturing a mold by providing at least one polymeric board material and removing, according to a computer-aided design, by CNC machining at least a portion of the polymeric board material to form a reverse image of a desired article to be molded. Preferably, the polymeric material has a glass transition temperature then less the molten temperature of a thermoplastic molding material to be injected into said mold. The polymeric board material can be a cured polyurethane-forming composition or a cured mixture containing at least one epoxy resin having, on average, more than one glycidyl group per molecule. The thermoplastic molding material is preferably selected from the group of polypropylene, acrylonitrile-butadiene-styrene copolymer and polycarbonate.
A further embodiment of the present invention is a method for manufacturing a prototype by providing a mold prepared from a cured polymeric material having a glass transition temperature less than the molten temperature of a selected polymeric molding material and injecting said selected molten polymeric molding material into a cavity formed according to a computer-aided design within the mold to produce the prototype. The present invention further relates to a prototype resulting from this method.
A still further embodiment of the present invention is a method for manufacturing a prototype by providing a mold prepared from a cured polymeric material and injecting a selected molten molding material into a cavity formed by CNC machining, according to a computer-aided design, within the mold to produce the prototype. The present invention further relates to a prototype resulting from this method.
A still further embodiment of the present invention is a method for manufacturing a functional prototype of a final article made from a selected polymeric material by providing a mold prepared from a cured polymeric material having a glass transition temperature less than the molten temperature of a selected polymeric molding material and injecting said selected molten polymeric molding material that is substantially identical to the selected polymeric material for the final article into a cavity formed according to a computer-aided design within the mold. The present invention further relates to a functional prototype resulting from this method.
A still further embodiment of the present invention is a method for manufacturing a functional prototype of a final article made from a selected polymeric material by providing a mold prepared from a cured polymeric material and injecting a selected molten polymeric molding material that is substantially identical to the selected polymeric material for the final article into a cavity formed by CNC machining, according to a computer-aided design, within the mold to produce the prototype. The present invention further relates to a prototype resulting from this method.
The present invention further relates to a polymeric mold for manufacturing prototypes and functional prototypes prepared from a cured polymeric material comprising at least one epoxy resin having, on average, more than one glycidyl group per molecule, an epoxy-isocyanate composition or a polyurethane-forming composition.